This invention relates to cartons or containers and more particularly to a gable top container. Such containers are usually fashioned from a unitary blank of paperboard or other resilient, stiff and foldable sheet material, usually plastic coated on both the inside and outside forming surfaces. A carton is made from a blank by scoring the latter to define fold lines or axes and then folding, forming and sealing it into a tube like structure, with one end, usually the bottom, then being closed and sealed. Thereafter, a foodstuff to be packaged, such as milk or fruit juice, is poured into the open end of the container and the container thereafter sealed at the top by infolding the top closure panels and sealing certain surfaces of these panels by means of heat and pressure to partially melt the polyethylene coating on the paperboard, the polyethylene thus also functioning as an adhesive.
The upper end of the usual milk or juice containing gable top container includes a ridge or fin, lying in a vertical plane, the fin formed by the lamination together of the uppermost portions of the two infolding or gusset panels and the uppermost portions of the two gable panels. The upper portion of the gable panels forms the two outermost fin forming panels, while the upper portions of the gusset panels form the two innermost fin layers. At the middle of the fin, where the two gusset folds oppositely meet each other, the effective thickness of the fin may be considered as of only two layers, these being the gable panel upper portions. For the opening of most types of gable top containers, the user, with the thumbs, pulls apart an inverted V-shaped opening at one upper side of the container, causing separation of certain seams, and then pushes inwardly on the sides to form the usual pour spout from one of the infolding panels, the latter having been provided with an adhesive to prevent a fiber tearing bond between the spout lip forming surfaces of the pour spout. With this type of opening arrangement or construction, proper alignment between the two outermost fin forming portions of the gable panels is not critical. In certain types of containers however, such as the extended shelf life foodstuff containers of this invention, an adhesive cannot be used.
In a different type of gable top container, opening is effected by the provision of aligned vertically extending tear lines in the upstanding fin (the latter having only two layers instead of the usual four), the lower edge of these tear lines meeting horizontally extending perforations on lower gable panel portions, at the base of the fin. Such a construction is shown in U.S. Pat. No. 3,339,820 issued to Krzyzanowski. If the sheet material from which the carton is formed is relatively thin, any misalignment occurring between the two outermost fin forming panels (each carrying its own vertical tear line) at the time the fin is formed by lamination, is not particularly critical. Vertical tearing can be initiated and take place.
However, if relatively thick paperboard is employed to form the carton, proper alignment of the fin forming upper portions of the gable panels becomes critical. Namely, unless properly aligned, the vertical tear line of one fin forming portion will not be properly aligned with the counterpart tear line on the other fin forming portion. In such a case, opening will become difficult if not impossible.
Misalignment between the fin forming portions of gable panels often occurs due to the difficulty of closing and sealing a filled container consistently the same way with existing top forming machinery.